The present invention relates to a multiband high-frequency switch that is mainly used for mobile phones.
In electric waves for mobile phones, two frequencies are set in two different frequency bands (for example, 800 MHz band and 1.8 GHz band), respectively. The two frequencies in the respective frequency bands are used for transmission and reception, respectively. Each mobile phone is provided with a multiband high-frequency switch for distinguishing between the respective transmitting and receiving signals in the above-mentioned two different frequency bands. A conventional multiband high-frequency switch 101 is shown in FIG. 6.
In the multiband high-frequency switch 101 shown in FIG. 6, the frequency of the transmitting signal to be sent to an antenna port 105 and the frequency of the receiving signal to be input from the antenna port 105 are diplexed to their respective frequency bands by a diplexer 102. The signals in the respective frequency bands, diplexed by the diplexer 102, are transmitted to single-port double-throw (SPDT) high-frequency switches 103 and 113. In the high-frequency switches 103 and 113, the signals having two frequencies are switched to a receiving signal and a transmitting signal, respectively, by diodes 19a, 19b, 19c and 19d operating as switching elements. The receiving signal is transmitted to receiving ports 113a and 123a, and the transmitting signal is input from transmitting ports 113b and 123b. Surface acoustic wave filters 120 and 121 are connected to the receiving ports 113a and 123a, respectively. Filters 121 and 122 are connected to the transmitting ports 113b and 123b, respectively
In this conventional multiband high-frequency switch 101, a circuit block is provided for each of the diplexing and switching functions. Hence, one diplexer 102 and two high-frequency switches 103 and 113 are definitely necessary. For this reason, the number of circuit elements constituting the diplexer 102 and the high-frequency switches 103 and 113 is very large, whereby it is difficult to make the multiband high-frequency switch 101 compact.